From ad3a19e6372b1e667128ed1ea2f49919884587e1 Mon Sep 17 00:00:00 2001

From: Akira TAGOH <akira@tagoh.org>

Date: Thu, 17 Feb 2022 17:30:12 +0900

Subject: [PATCH] Fix the stack buffer overflow issue

strlen() could returns 0. Without a conditional check for len,

accessing S_ pointer with len - 1 may causes a stack buffer overflow.

AddressSanitizer reports this like:

==1219243==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffdce043c1f at pc 0x000000403547 bp 0x7ffdce0

43b30 sp 0x7ffdce043b28

READ of size 1 at 0x7ffdce043c1f thread T0

    #0 0x403546 in main ../bin/fribidi-main.c:393

    #1 0x7f226804e58f in __libc_start_call_main (/lib64/libc.so.6+0x2d58f)

    #2 0x7f226804e648 in __libc_start_main_impl (/lib64/libc.so.6+0x2d648)

    #3 0x4036f4 in _start (/tmp/fribidi/build/bin/fribidi+0x4036f4)

Address 0x7ffdce043c1f is located in stack of thread T0 at offset 63 in frame

    #0 0x4022bf in main ../bin/fribidi-main.c:193

  This frame has 5 object(s):

    [32, 36) 'option_index' (line 233)

    [48, 52) 'base' (line 386)

    [64, 65064) 'S_' (line 375) <== Memory access at offset 63 underflows this variable

    [65328, 130328) 'outstring' (line 385)

    [130592, 390592) 'logical' (line 384)

This fixes https://github.com/fribidi/fribidi/issues/181

---

 bin/fribidi-main.c | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/bin/fribidi-main.c b/bin/fribidi-main.c

index 3cf9fe1..3ae4fb6 100644

--- a/bin/fribidi-main.c

+++ b/bin/fribidi-main.c

@@ -390,7 +390,7 @@ FRIBIDI_END_IGNORE_DEPRECATIONS

 	    S_[sizeof (S_) - 1] = 0;

 	    len = strlen (S_);

 	    /* chop */

-	    if (S_[len - 1] == '\n')

+	    if (len > 0 && S_[len - 1] == '\n')

 	      {

 		len--;

 		S_[len] = '\0';